Gotta say I enjoy the sculpt of the Inceptors. The trick's going to be getting the most out of them. As with the Inceptors, they compete with some other units an in interesting way, and it's about options.
Inceptors - The Basics
Squad Size - starts as three guys, and can bulk up to a six-man squad per Fast Attack slot.
Weapon Options - they carry a pair of guns. Bog-standard gear is a pair of assault bolters (translation - take a heavy bolter, cut the range in half and switch it to assault 3 vs. heavy 3). If you feel like dumping a chunk of points on them, you can swap the whole squad's bolters out for plasma exterminators. They're assault 3 plasma cannons with half the range.
The guys have no specialized melee weapons, but can deal a mortal wound on a 6 on the charge. This is not what we'd call 'reliable.' These guys are guns on jet packs, but melee is a partial consideration.
Mobility - you've got a base 10" move, and Meteoric Descent lets you set up in reserves and drop in no closer than 9" away.
A Note on Durability - As with all primaris, they've got two wounds per bob with the typical marine 3+ save. However, you do have T5 on top of that - so you're a little more resistant to small arms than the average Marine.
Battlefield Role
Your choice in guns here is really going to determine your use.
Assault Bolters - these are the cheaper option. You have a good volume of fire at six shots per Marine, and S5 / AP-1 / 1 damage is a useful profile. A minimum-sized unit cranks out 18 shots (12 hits on average). These guys can do a number on infantry. Also, in a pinch you can knock some wounds off of vehicles. It's not ideal, but a T8 3+ vehicle will probably lose a couple of wounds to a full squad shooting.
Short version - assault bolters are more for killing troops, but in a pinch can soften up or finish off vehicles/monsters through volume of fire.
Plasma Incinerators - these are pretty expensive. You are, however, paying for the ability to drop a pair of plasma cannons per marine when and where you need them, and get the first volley in. Each dude fires 2d3 plasma cannon shots - It's either S7/AP-3/1 damage, or S8/AP-3/2 damage (and die on ones).
Note that a squad of these guys is probably going to melt high-value targets. Math is a little tricky because you're rolling number of shots, then rolling to hit, then to wound. You can fire as many as 6 shots per guy or as few as 2. AP-3 means that heavy-armor troops and vehicles should be concerned - things like Terminators and Knights are going to be taking their invulnerable saves unless they're in cover.
Note also that you probably want a captain nearby - if you're going to do anything other than murder one-wound infantry (and frankly, there are PLENTY of ways to do that with cheaper troops) you're gonna want to overcharge. Each Incepter with plasma incenerators is almost 90 points - and overcharged guns kill them. You really, really want to re-roll those 1's. You might consider a deep-striking captain (Terminator armor or jump pack), but with 18" range you might also be able to get away with taking a captain on the board that's mobile.
On purely average dice, a squad of these will knock out 4-6 wounds off a T8 3+ statline. If you're fighting T7 or less, you're going to up that to 6-8 wounds, which translates to "I think I just deleted a 150-200ish point model".
Overcharged plasma on terminators and the like is just kinda hilarious to watch - each failed save is a dead 45+ point model, and it's not hard to delete a small unit.
Short version - it's risky, but bring re-rolls and plasma incinerators can melt multi-wound infantry and seriously maim vehicles.
Compared to other troopers
1) Assault Marines
Inceptors are their shooty cousins. The best comparison would be assault bolter Inceptors versus Assault marines - both are going to go after infantry. Inceptors do it from range; assault marines need to get into hand-to-hand.
You can get a full ten assault marines (and probably a melee upgrade on Sarge) for the price of a minimum-sized inceptor squad.
In melee, the assault marines put out many more attacks - each guy's good for a couple of swings, and they probably got pistols on the way in. Sheer volume of attacks is going to do better than the assault bolters, but note carefully that assault marines are going to end up putting themselves into the thick of it, and be open to retaliation. Melee is a risk - there's the part where you're asking to get both shot AND punched, versus just shot. And make no mistake - you're going to spend time in charge range.
Furthermore, unless you're Black Templar, your odds of assaulting out of deep strike are somewhat iffy - BT can swing it around 48% of the time, whereas everyone else is looking at a ~28% chance - not so great.
Assault marines do better when it comes to volume, but Inceptors are much more likely to get the first strike off, and less likely to get counter-assaulted. Durability is a bit of a wash; six T5 wounds vs. ten T4.
2) Land Speeders
A couple of land speeders with heavy bolters is about the same as a minimum-sized squad of assault bolter Inceptors. The tradeoff here is in the platforms and range.
Land speeders have more wounds and a worse save (T5/W6/4+) with the same toughness. The big difference in their durability is in range - speeders can sit back at 36" and dump shots, whereas the Inceptors are going to have to be much closer.
The big difference here is in the range - Inceptors are close enough to draw fire from just about any source, whereas Land Speeders can sit back. Land Speeder durability is based in part on the rest of the army - they're kinda allergic to heavy weapons, but if they're one of multiple targets then they're probably less likely to get murdered at range.
Mobility is an interesting comparison - Inceptors can move and shoot without penalty, but Land Speeders take a -1 because Heavy Bolters are, well, heavy weapons. That being said, Land Speeders have a 16" move, while Inceptors have only 10".
Overall, this one's an army composition comparison - speeders need to be part of a target-rich army to make sure they aren't the only ones taking heavy fire, whereas the Inceptors can get the first strike.
3) Heavy Bolter Attack Bikes vs. Assault Bolter Inceptors
Heavy bolter attack bikes are comparable in points - the firepower and mobility are different. Bikes have better base speed and turbo-boost, but have no way to get around the -1 penalty for moving and shooting heavy bolters. Heavy Bolter bikes are more durable per model (T5/W4/3+), but also have less firepower (a heavy bolter and a twin bolter vs. two assault heavy bolters).
Inceptors are also likely to get the first strike. I'm leaning towards Inceptors here because of the first-strike capability, and because they've got a little better mobility. I feel like you might as well go with a double heavy bolter Land Speeder over a heavy bolter attack bike.
4) Multi-Melta Attack Bikes vs. Plasma Incinerator Inceptors
Ah, now we're finally getting around to throwing the plasma inceptors. Costs are similar. The inceptors can throw more dice, but the attack bikes through much scarier dice. The bikes have the speed to get within 12" get multi-melta dice. The problem is that they're only throwing three dice with a 50/50 chance to hit. You are also asking to get shot up or tied up in assault.
The major advantage that the bikes have here is cost - they're about 20 points cheaper a head than Plasma Inceptors. Both sides really, really want re-rolls to hit.
While multi-meltas are pretty scary, I'm leaning towards Plasma Inceptors because of weight of fire on this - who cares if you do 1d6 damage if you're only putting out a few shots?
5) Shooty Terminators vs. Assault Bolter Inceptors
I'm comparing these options because they're both around to drop in and shoot. The difference lies in what they do
after popping up and shooting. Terminators punch things and hold ground; Inceptors either avoid melee, or break away and shoot. Terminators also really kinda mess things up in melee with powerfists.
If you want a drop-and-shoot option, your decision here is based on what you want to do afterwards. Also, if you're Black Templar, consider the fact that you've got almost 50/50 odds to make it into assault when you arrive, so there's that.
In Closing
Inceptors are a fascinating addition to the marine army. They provide you with a solid deep-striking shooty option that remains mobile after its arrival. The assault bolter ones are workhorses that can thin out infantry and do a little damage to vehicles. The plasma-toting Inceptors are significant threats to expensive targets - but are costly and really require re-roll support to avoid being a threat to themselves. They're also a bit dice-reliant since they have random numbers of shots.
I lean towards assault bolter inceptors myself because of the price, and the fact that they aren't asking for re-roll support.
