A couple of things you need to remember about human nature (and subsequently these forums) is that it's usually the unhappy folks that are the most vocal. If you go to a restaurant and have a bad experience, you're much more likely to get on Yelp and bitch and moan about it whereas those that have an average to good experience most likely won't bother to lift a finger to give the restaurant a good review. It's just the way we humans are wired.
Tying this back to the Impact - I've had two of them (a .25 in silver and a .22 in black) and had a great experience with both. I only kept the .22 because I have several other .25's already (and I plan on picking up a .25 barrel/probe set down the road when they're more readily available and cheaper). The ONLY legit complaint I have is the incredibly stupid design of the foster fill fitting - which is damned near impossible to detach from the rifle after each refill. How they let this pass is beyond me.
Other than that, the other complaints I've seen are about the rail not being to mil-spec which doesn't bother me since I only use two piece mounts. Some people complained about leaks but, guess what, pretty much every brand has leaks for one reason or another so it's not like this is an issue only isolated on the Impact. Neither of mine had a leak. Both were very accurate and consistent; the only limiting factor is my shooting skills. The extendable shroud works very well and I did not notice a change in POI from extending it or removing/replacing the barrel. That big but light CF bottle gives you plenty of shots and you can even get extras to swap out in the field so you don't need to drag your airtank along. The rifle is very easy to adjust and break down and, thanks to it's modular design, I'm sure there will be custom parts available for it in the months to come.
All in all, the Impact is neck and neck with my .25 Vulcan as my favorite gun right now - beating out both my Edgun R3M and Colibri Hummingbirds (yes, plural). It's a very innovative design that is unmatched by anything else currently available so you have to give FX credit where it is due. Don't mentally give up on the Impact before you even take delivery on the package!
If you have any specific questions/concerns about anything in particular, let me know and I can try to answer.