Yes, anybody who has seen a few 100 animes will have the same problem....all you can do is wait for new animes to air...or just force yourself to check out all the average shows
It's more that once someone has watched 100 or so shows and formed opinions on all of them, they start to get more closed-minded. You start to think that this certain subset of the stuff you've watched was probably the best ever, and there's no way you'll find anything better. It might just be a different experience. That's also a bullshit way of thinking. You're painting the "good" shows as being much better than they actually were in your mind.
At some point, just stop and, after a lot of experience with watching, try to rewatch some of the stuff you've considered good. Do it with a completely open mind. Unbiased. Pretend you're doing it for the first time. Reanalyze everything, don't just assume it's good. It will probably still be
enjoyable to watch, but is it actually "
good"? There's a line between those two qualifiers.
You'll probably find that not everything you've watched is as good as you thought it was in the past. It may just be shit that you thought was "good", but it's actually just "enjoyable" based on your preferences. You'll probably also come to the realization that there's just as much value in watching something for being "good" as it is for it being "enjoyable" to watch.
Well, that's a theoretical schedule of events.
For instance... I've watched all of Haganai and Acchi Kocchi. Were either of them particularly amazing? Hell no. I enjoyed watching them, though. Just get your head outta your ass.
That's not to say I think that anime isn't worse than it was before, in general. Even looking at it objectively, I just can't find as many things that are seriously "good" these days. Best thing to do is to just go with what you can enjoy watching. I think part of what's ruining anime is moe. Not because I hate moe in general, but because it seems to me like studios realized that appealing to those goddamn type B's makes them a hell of a lot more money than appealing to type A's (who probably manage their financial assets better). Even stuff that can be considered "good" these days will probably still put a bunch of ecchi and/or moe shit into it because it sells.
Why do I type this fast?