Well, i personally enjoyed most of them right up until Project 8 (with a few inbetween not exactly been stellar)
My scores for the Hawk series.
THPS 1....... 85%
THPS 2...... 88%
THPS 3...... 95% (easily the best in the series, big step up from THPS 2, fantastic challenges, great specials, amazing level design and one of the best soundtracks of ALL TIME in a videogame, a true masterpiece)
THPS 4...... 82%
T.H.U.G... 92%
T.H.U.G. 2... 75% (didn't like the jackass humour at all, and level design was poor IMO)
American Wastreland..... 90% (a return to form for the Hawkster here, great level design, good challenges, FANTASTIC soundtrack)
Project 8..... 93% (played in on both Ps2 and 360, 360 version had online multiplayer aswell, so that helped with its high score, again for me this one had great level design, and the new slow mo air tricks were very cool)
Proving Grounds..... 50% (all that taking pictures of yourself whilst pulling off tricks really killed it for me, also the levels were frankly boring and it was the worst soundtrack yet)
I just want to play ONE MORE extreme sports game where you used the D-pad to pull off tricks as opposed to the analog, i hope that activision can make this happen, but unfortunatley, i feel as though that boat has sailed on by 
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