Invisible, Inc., as a round-based-game is very well done. It has a thick atmosphere, and nice, always new levels, and a well balanced skill-tree. The presentation is technical, and fits very well. If you play heavily guarded levels, you will also experience some nice RPG-reminiscents, like the floating guardian. Reminds me of Eye of the Beholder.
So, what is the problem? IF you get to later levels, the guards heavily outnumber your team. It's not 2:1 or 3:1, that could be handable. But in the latest level, I played, I was outnumbered by at least 4:1, and of the guards woke up after one round already - he guarded the CEO of the company to hack. Dealing with a 3 turn cooldown on your main weapon, you are - let's say - always dead. This said, even in easy mode, which i was playing for about 12 hours now, the game always ended after 5 missions. Interestingly, by doing maps randomly, frustration about this is not as high, as expected, as you need to improvise.
I know, it's supposed to be a hardcore stealth game, but the difficulty is much to high, even after playing about 30 easy missions, in said 12 hours. However, I'd recommend this game to lovers of round-based, agent, difficult missions.