I look upon ET and trem as kinda equal, though trem has some features i'd like to see in ET, such as the friend search.
Though there is more depth and strategy on some levels in et, trem is more intense and fast-paced. this can go both ways for both games really... when i play et, i can hang back, and consider, help in other ways than slaughtering the other team, i can distribute ammo, revive people, take out dangerous mortars and so on as covert ops.
Really, i think et is a better game, but it is also older, so there are MANY MANY players there who are just too good, it gets boring playing against godlikes sometimes..
trem is very addictive in the way its played, bases and so on, but i find it just a little bit too fast paced for my taste though 'tis fun really, the speed- it just gets tiring after some time.
I very much like experimental base building in trem, i can waste hours on an empty server on finding new working base locations.