Yeah, I'm the exact opposite. Games like Commandos are way to hectic for my minimal hand-eye coordination. I like to sit back and thoroughly examine the situation before deciding on a plan of action. It's TBS all the way for me. And, honestly, RTS games are the majority, and TBS fans are the freaks. Just look at the ratio of RTS to TBS and you can easily determine that. Thankfully, games like XCOM, Jagged Alliance, HOMM and Silent Storm provide a lot of gaming goodness even if their design is the exception rather than the rule.

For shame, you can sit back and relax with commandos, sometimes. :D What I like about Commandos as opposed to JA or XCom, when I sneak up on someone I know that (unless they suddenly turn around) I can actually get to the guy and take him out. I don't have to worry about running out of movement points and then having to sit there hopelessly still as the guy makes his moves. If I need to get from point A to point B I click on point B and go there, I don't have to sit down and calculate how many steps it's going to take and the fewest amount of steps needed as opposed to where the best stopping position would be and etc etc etc. Little too much math for me.

Tyrian Story campaign on easy / Normal difficulty :)

Blackwell series

Prince of Persia (the one on GOG not the reeaally old reaaally difficult one) is so easy it almost plays itself. Controls seem a little off for my liking. It does take a little while to get used to it. But it's so gentle that you can't get frustrated with it.

Even the "elevator" section where the princess keeps shooting you with arrows as you try to defend her from about 30 enemies? I got through that once and even then, it felt like a fluke. Then again, I'll willingly admit that I don't actually have any game playing skill at all.
Well, if we're recommending adventure games, the Telltale games are all rather easy. Walking Dead (though not on GOG) nearly plays itself.

Reus would appear to meet your requirements. Ya should give it a go. It gets hard later on but its a "go away and think up strategies" hard not a "you have been turned into a sieve by Russian gangsters start again" sort of difficult.

Hotline Miami.

Seriously though, like others have said already, Torchlight is probably what you're looking for.

What about Silver? I didn't play it for long when I gave it a go bit it seemed pretty simple and fun, dunno if it suddenly gets crazy later on...

Broken Sword for an easier adventure and Incredible Machine if you want a casual toy

I completed Outcast years ago and was sad there wasn't any more when it finished, I don't remember it ever getting crazy hard but its been a while...
Nox has that Diabloesque vibe too

:D

But is it "fun game"? I am playing episode 4 now and it really plays itself and it's very good series but the last thing I would say about it is that it's jolly.

It's an adorable game. I enjoyed taking photos for a botanic institute and having animal friends :D. Blackwell series is a good recommendation. It's playful yet later in the series it gets more serious. I don't mind, just saying.

Trine 2 fixes what is so sorely missing in Trine, which is a save game system (although it is still rather too simple for my taste). Sadly Trine 2 is not yet on GOG.