A game should not make you replay a section (a good 30 minutes worth of a section) when you've clearly demonstrated that you can go through it perfectly.  Also I beat like 10 of the bosses and didn't die too much but honestly I just got annoyed with the targeting and replaying of the easy parts just to get to the hard parts.  There should be a checkpoint before the final boss.  If you want to give me just as much health as I had before then fine.  I don't mind a challenge.  I've platinumed a lot of games (most require you to beat on hard).  I've beaten really difficult 8 and 16 bit games, but damn I hated that lack of checkpoints.  It just felt like they were artificially extending the game's hours by making me replay easy parts again and again so that by the time I got to the boss I didn't remember the right strategy (eventually I found that most of them had easy ways to beat them with the environment).  Bottom line is I didn't stop because of difficulty.  I had just beaten a giant dragon that you to harpoon and when I did I basically thought to myself "I am not having fun with this" and sold it.

That giant cerberus and centaur combo near the end of GoW3 had me ready to strangle my dog.  Zeus seemed like a cakewalk by comparison.  Although GoW2 was the most challenging plat because of the "kill 10 enemies in the air" challenge.  I got it on about my 100th try with 0 seconds showing on the clock.  Thought I had missed it because there was a zero and then cried tears of joy lol