The show is interesting. I love the concept, but as someone else said, it's executed poorly.
There's too much trash-talk. They try too hard to make it a "Spike TV" program, or in other words, the people try too hard to be tough and "manly". Yeah, it's for adult men, but seriously, it's not like everyone's dumb. Basically, the guys come off as ridiculous fanboys that remind me of those on the Internet.
Also, the tests are NOT similar at all. They're totally different in all cases, and sometimes is unfair/too biased. For example, the grenade test in Green Beret vs Spetsnaz - One grenade was next to dummies in an enclosed room...the other grenade was inside a laundry machine with targets outside. Didn't we learn in science courses that tests should be similar to truly compare two things?
Then there's the case of questionable research, but that's up for individual opinions. Some people say the show is more like "Deadliest Weapon", others say different things.
Lastly, they need to match up warriors more fairly. We should be seeing similar fighters fighting each other, not totally different ones. I know having crazy match-ups is cool and all, but they're often one-sided. Spartan vs Gladiator or Apache vs Ninja would be more entertaining and much more of a guessing game. Otherwise, a lot of the match-ups were way too obvious in terms of who would win or not. The gun ones (Mafia/Yakuza, Green Beret/Spetsnaz, IRA/Taliban) were the only ones I could not predict correctly, because those were actually even match-ups.
One thing I never understood: They say the show isn't "Deadliest Assassin" or "Deadliest Distraction" - so why bother having a Ninja up there at all, especially when we KNOW they don't fight up front?