I actually don't think shooters have necessarily gotten better with time. Personally I find the whole "aim and shoot" thing kind of annoying. I prefer arcade-style shooters, like Wolfenstein ET (which I still play every now and then). Really, it's just better graphics and then different ways of shooting. It's not necessarily better. It
is probably evolved.
What I dislike most, though, is how series tend to go. Here's my little rant about that; I made it a long time ago, and just put it in a notepad file for later use (I have a bunch of those little memos floating around my computer). I think it was actually meant for another topic, so some material isn't relevant:
Mass Effect 2 and 3, Halo 2, 3 and Reach, etc.
I think this little "LET'S MAKE A FUCKING METRIC SHIT TON OF SEQUELS" bandwagon is killing gaming, personally. You get the first product, which is the thing that gets the series started, and it might be rough around the edges. It's more of a love-it-or-hate-it kind of experience that's not necessarily the best, but it's still pretty good, and starts off the hyping and popularity for the second game...
And that's where things go wrong.
They just keep watering down the experience to where more people can play it. Generally speaking it might be a "better" game, but to me it still sucks more. It's them going "how can we milk the name better?" They'll make something that may please critics and general gamers, so it's hard to say it's worse without drawing fire.
IMO series that were done right were stuff like Tales of <insert>, Disgaea, Otogi, and Kingdom Hearts (though, KH2 did dumb down the battle mechanics a bit). SSB -> SSBM wasn't that bad, but then I played Brawl and I didn't really care for it much. The action felt slower, like it had been dumbed down for the Wii community.
While I do think a lot of games today are just like "Hey, let's make really good graphics and generic gameplay and put some violence in it, and call it an amazing game", that series business is what annoys me more.
Also, if you guys haven't noticed, there is a serious influx of MMORPGs. Like seriously, after seeing all of those F2P companies like Nexon making big money while practically ripping their customers off, I'm seeing more and more series start to go over to it.
What's worse is that a lot of them have pretty generic mechanics. I haven't played anything recently that made me go "oh man, this is actually cool." All of them just reuse generic mechanics.
I don't necessarily think that games are getting dumbed down, but series cashing and MMORPGization is hurting the industry.