man ive only had a few games of this so far, but it is very similar to SSHD, only on an open-plain type of map and, so far, much much harder! heaps more weapons, but you have to earn them and "rank them up", with a semi-complicated weapons system.
plus instead of fighting crazy-coloured aliens and rocks, you're blowing up enemy ships and enemy bases.....and ive only just reached the aircraft carrier-type thing towards the end of stage 1 (well i hope its the end), playing on "recruit" too 
geez i feel like a noob. but it also gives me confidence that this game will provide a much longer lasting challenge than SSHD, which i kinda felt like once i knocked off the first planet, the rest started to fall in fairly quick succession.....then it got real boring.....until the patches came along of course! 
but as for Novastrike, once you get used to the slightly different controls, its yet another successful addictive game by the PSN 
Call of Duty 4: Modern Warfare
24/07/2008 / "Don't worry about avoiding temptation, as you get older temptation will avoid you." W.Churchill