Okay, here we go.
Loki is largely regarded as a more evil figure by the end for a few reasons. His random killing of Blader, for his amusement, which was largely the straw that broke the camels back for the rest of the gods since he'd been toeing the line of getting killed for a long time. Like the time he thought it would be funny to shave Sif's head. Sif, who was the wife of Thor. Thor, of the famously short temper. Great plan buddy! He managed to squeak by on that one. The big reason he wasn't thought well of was that he was untimately a traitor to his kind. I mean, he's the one god who would march on the side of the giants come Ragnarok.
Odin was also not as popular as you might have thought, since one of his other naems to be known as was the Betrayer of Warriors. Odin needed warriors for the final battle, and was thought to let some of the best warriors of the land die in battle before they rightly should so he could have them. The more popular god was actually Thor, since he was a more down to earth kind of god whose main focus was beating th ever loving crap out of people.
As for reneging on deals with mortals, well...he is leader of the panteon of gods. The mortals who bargained with him might have really wanted to think twice there. It's kind of hard to force the leader of your gods to make good on a deal. And to put a bit of justification on Odin, he's playing a much bigger game than the mortals. For all they know, his flaking out on a deal might have ended up being a piece in the puzzle of his trying to save Asgard from the Last Battle.
On the subject of the Last Battle....
Loki is not the main architect behind Ragnarok. At that point, he's just another part of it all. Sutur, lord of the fire giants, and Thrymm, lord of the Frost giants, were the two major players, Sutur a bit mroe so I think, seeing as he was to burn most of the world on his approach to Asgard. Midgard burns, and the Nafalgar, the ship crafted of dead men's nails, leaves hell loaded with the unworthy dead. Fenrir swallows the sun, and would kill odin. The World Serpent rises fromt he depths to face Thor, one last time, to be killed by him, but slay the god as well through poisoning. Loki is ultimately pretty small in his place in the whole thing. Heimdall, the god who watches over the rainbow bridge that leads to Asgard ultimately kills him.