1) It has horrendous requirements for a game that looks worse than Fallout 1 and by that I not only mean hardware but also software.
It requires .Net Framework 4 which weighs more than the game itself AND Windows Media Player installed. WTF?
Compared to
Age of Decadence (which even a noob like me can run on linux and doesn't need additional shit that weighs more than the game itself just to run it) it looks amateurish at best. Not to mention that AoD is far more inventive, has more unique setting, way better dialogues (in that regard only Fallout 1 or Planescape: Torment can compete) and more interesting characters and story. Plus the fights are much more enjoyable. The only Underrail advantage is the price but I can see why now. Styg is lying in the minimal requirements section, "Win XP SP3" is not enough (I had had that, I also had .Net Framework but older version and until Underrrail every decent program worked just fine). So in order to make this game work, unless you have more than 1.2 GB of free space you need to use gparted (or some other good "partition magic" clone), change the size of your windows partition, install shitty WMP and then and maybe then it will work.
It's a non-issue for me now that I've upgraded my computer but it annoyed me a lot when I was installing it on my old computer where I've purposefully had a C partition small, for essential programs only (I've also had system restore turned off and other things done). All of that so that I could install a game where I don't even see what's next to me (walls often obstruct a view so you don't see a locker or remains or other things).
To clarify, I don't have an issue with obsolete graphics, I have an issue with improper system requirements for such graphics and more to the point with requirements of additional shit being installed. The only thing Underrails lacks is Windows Live account required to run it...
2) You can't load a game during combat unless it's your turn. It is annoying especially when you know for sure you will die before even all the guards will have a chance to burst ammo in you. No such problem in AoD.
3) If you want to sell your stuff you have to go from one vendor to another because one trader will buy only very specific things and nothing else. Which makes sense in real life but in a game it's annoying (and to be honest in a post-apocalyptic world I doubt any trader would pass on a chance to buy something he doesn't need at the moment but for a fraction of it's real value). AoD wins again.
4) Running is so slow in here and it's one of the main reasons I don't want to replay the game. Playing Underrail lets you realize how great "teleporting" is in AoD. First location (SGS) is very annoying, especially cave tunnel exit which is slow like a retard. Also, you can't skip the shooting session with Gorsky (Polish surname BTW and a plus for Styg for choosing such prestigious one
).
5) There aren't that many ways to accomplish missions and pickpocketing skill is a must have. AoD gives much more freedom to the player and always gives you more than 2 options. Here there are usually 2 options only where the second one is way more difficult than the first (e.g. retrieving Elwood's key).
6) It has too monotonous locations. Corridors, corridors and some more corridors. That is the main reason it's not as replayable as AoD.