I'm not that into the RE movies, but they are fun popcorn flicks. RE4 is a masterpiece, and most of the time I feel like it's not connected to the movies at all (i mean, it isn't really <_<)
Actually, besides Leon, Ada, and Wesker's voice being in the game, RE4 doesn't have much of a connection with the other games as well. No zombies at all, just really smart parasites.
The movies are decent I guess. I'll probably see RE3 in theaters and see if it's worth a buy from that point. The first one was okay, it had more of a RE feel, IMO. With the second one, it was more of a action movie instead of the regular horror thing, like "OMG, that zombie is trying to bite my freaking arm. AHHHHHH!"