The games vary in quality, but are generally pretty good to excellent. I could never get into the original series due to the clunky camera and controls, but once they went to over-the shoulder (RE4), it became a favorite. Resident Evil 4 in fact is one of the best games ever made really - it's Top 10, maybe 20 depending on how you are counting, but is just excellent, excellent, excellent!
I haven't played all of the games but have done most of the earlier ones when I was younger. Have tried replaying them as an adult and they genuinely terrify me. More so than watching a horror film. I just wish the RE films lived up the games especially the original few.