I try not to get excited for upcoming games anymore because this has happened far too many times for me. My list may be a bit old-game-heavy because of it. There are rare exceptions, and a couple things still make me a bit anticipatory, but I've been lucky (or clever?) enough to not be disappointed in a while.
On to the list (Warning: subjective opinions ahead!):
I got into this one pretty late, only having played it within the last couple months. The concept is interesting but I just found no fun in playing it at all. The driving feels a bit off - less Rockstar feeling, more "obligatory car-chase level" feeling.
System Shock was my absolute favorite First-person computer game, and was actually the first FPS I ever played on a computer. A menacing atmosphere where you never felt safe anywhere, incredibly dangerous and varied enemies, an interesting environment that felt real, fun abilities and weapons, and one hell of a creepy villain all came together to build a game that I've been trying to top for two decades now. Bioshock was nothing. Generic console-port shooter with a reasonably interesting setting and kind of an interesting villain (unfortunately, you had to actually get near the end of the game to realize just HOW interesting he was - so for most of the game, there's no real impactful villain at all) but absolutely uninteresting combat, abilities/weapons, plot, enemies. Huge freaking letdown. The sequel was even worse. The sequel's sequel was even WORSE.
What looked and seemed like a pretty goofy title with a very clever and versatile magic system actually was one of the most cumbersome and unenjoyable game mechanics I've seen. I still think it could be done, but this isn't how. Maybe if they didn't slow down while holding elements? Maybe if the interactions were better explained? I'm not sure. There's a ton of promise, but it hasn't been properly accessed yet.
A beautiful and very interesting six-degree-of-movement, zero-gravity shooter that was very cleverly designed by a group of people known more for benchmarking software, Shattered Horizon was actually pretty damn amazing. And then a few months later, they patched it to death. At release, there was one gun that had multiple functions. Auto rifle, slow snipe mode, a melee bayonet, and three grenade-launcher types. Ice; basically a smoke grenade, EMP; flashbang-ish & removed your hud entirely when hit, and explosive; damaging but most importantly, could push players around - ie, out of their cover. switching between them at the right time was part of the dynamics of combat, and it was a really unique and slightly iconic weapon system. The patch split that one gun into a bunch of guns which all felt like every gun ever in every other shooter that ever existed (Railgun, Machinegun, Assault Rifle, SMG and Shotgun, oh boy.). Even worse, you had a limited selection - you picked one at the start of each life, and that was it. Stuck in a situation that your gun can't handle? Fuck you. Need to adapt to a changing combat situation? Fuck you. The game, of course, died very quickly and never came back. A goddamn shame.
An interesting concept, totally fascinating setting and theme. Except the gameplay is self-defeating. You have a limited resource, power. Anything you do uses that power. So the less you do, the better off you are. It's a game that doesn't want you to play it. It's not difficult, it's just annoying. And then add in how quickly jump-scares lose impact compared to the long-lasting pervasive dread that a creepy well-established atmosphere has, and the game loses all impact very quickly. And then the sequel was just more of the same mechanic again. And the next one will probably be the same. I can't blame the dev for sticking with what works, but I can't help but feel it's missing its potential by sticking to the same self-defeating mechanics.