Deus Ex Invisible War is the only game on the market (that I can think of), that allows for such open-ended gameplay and complex problem solving.

Agreed, it's just unfortunate that the level design and difficulty balance didn't choose to exploit IW's greatest strength. There is no situation in the game where it is necessary to come up with a creative solution to problems, the easiest way is always shooting or activating the cloak biomod. This weekend I've been playing through IW yet again, only this time I'm playing around with what you can actually do with the game systems and am having a whole lot of fun with it. Two examples from the Tarsus Raid level:

There's a little sequence where two Order Seekers try to kill a pair of scientists. While you can shoot them down easy enough, you do have a few seconds to come up with some other solution. Here's mine: I rolled one of the gas barrels to the base of the nearby stairs and then placed a proximity mine right next to it. The first Order Seeker was killed by the blast from the mine. The mine also had the effect of blowing up the gas barrel and enshrouding the second seeker in poison gas. Going to those lengths to kill the seekers was totally unnecessary, shooting them is far simpler and just as easy, but it was far far more satisfying.

A little later you come across a room with two Seekers patrolling it. I used the Bot Dom mod to possess a spiderbot patrolling a nearby airvent and then manuevered the thing into the center of this room. I then went back to a previous room and grabbed a flask and then threw it near where the now disabled spiderbot had been parked. The two seekers went to investigate the noise and when they got close to the spiderbot I fired a round into the bot causing it to explode. Both seekers got caught in the blast and died.

I'm having a blast replaying different sections of the game (that I've already gone through four times) but playing around with the game systems to create unique solutions. This is why I like this game.