When I think rogue-like, I think of a good, challenging (sometimes brutal), game that I can play in a couple of hours. I think of ascending difficulty where I try to find better gear and become more powerful so that I can attempt to defeat ever more challenging enemies until they kill me, or I manage to beat the end objective. Completing the game should be a proud moment that makes me want to brag to my friends that I finally accomplished it.
Sadly, Steam Marines fails to achieve most of this. The basic game mechanics aren't bad, and the the first couple of levels were fun, but it gets sorely repetitive very quickly. Each area introduces new enemies, but they all do pretty much the same thing (except the bosses, but even they only have a minor twist to make them unique). On the rare occasions when you find new weapons and armor, odds are your marines can't use it, or it will be worse than what you already have. Once you figure out how to beat the enemies, the game becomes very formulaic and more of a chore to trudge through each level. At normal difficulty, each level took about 30 minutes (that number can vary a lot). With 25 levels, it just takes way too long for a rogue-like.
When I beat the game, I wasn't jumping for joy. Rather, I felt myself saying "finally, it's done." I decided to raise the difficulty to see if it got better. The enemies were tougher and more numerous, but still did the same thing. The levels just took longer and longer to beat and felt more like a crawl. After a couple of levels, I decided I had better things to do than wait a minute or two between every turn while the computer made its move.
UPDATE: Changing the AI speed did help speed up the computer's turn significantly, but wasn't enough to reduce the tedium enough for me to want to play this game again. I got through a couple more levels and decided I'd rather spend my time playing something else. I do appreciate that the developers are still working on the game, so hopefully they'll be able to add enough variety to make me want to play it again.