Well, it's all relative to when they were released. I got RE back in March 1996, and frankly didn't like it that much. I thought the graphics were a mixed bag, and the game was a bit frustrating (choose the wrong path and you're fucked). I had a save just before the last boss with Chris, but I couldn't beat the last boss, and then that save got erased. A year later I played using Jill and finished the game, and appreciated it a lot more for its atmosphere and shock tactics.
But I was pumped for RE2, and enjoyed it a lot for its more action oriented approach. I guess replaying it over and over to get an A rank made me appreciate it even more. And I watched my brother unlock Tofu which was a damn impressive achievement.
I also liked RE3, and to this day don't understand the hate for it. Nemesis was a brilliant idea, and the game was even more action oriented than RE2. Those moments where you had to make a choice when ambushed by Nemesis were freaking intense.
My love for the series diminished when RECV came out. It wasn't bad, and it had higher production values than past REs, but it was more of the same, and I was getting tired of it. Still, I bought my GC when RE came out, and was really disappointed. Less of a remake and more of a bastardization in my eyes, it really had little in common with RE1.
RE0 was OK, but again more of the same. But I'm looking forward to RE4 since it's supposed to be a bigger step than any of the previous games were over their predecessors.
So in short, while I agree that the series has improved, it hasn't improved enough to keep my interest and enjoyment level as high as it once were. Here's hoping RE4 will change that.