There can be multiples of the bosses on the same map. Also the hard part is not just finding them, but finding them while getting enough upgrades and levels to actually beat them.
Since a lot of bonus points come from holding down the mouse button for the entire level, yes, it's pretty straightforward. However some of us were playing before badges were added, and had to go back to try other levels after previously not caring about highscores :P
nutshell: you get experience from every game win or lose; a high level doesn't necessarily mean they're any good, while new players can pick up the game pretty quick. yodudes567: plan your attacks better; I rarely end up with that situation.
Being able to check the map, even just the area you've already covered (and the quest objective if you've seen it) would be a great help. Could do without the 'rescue teh princess', I nearly didn't play the game.
Some changes I'd like to see: I still want to see in future versions the ability to play with either keyboard or mouse, rather than needing to switch between them. Keyboard shortcuts for the battle options would be a great start, even if you can't put in keys for all the spells and even if you still need to use the mouse for inventory. Alternatively, you could make it so we can move in dungeons with the mouse, same as for the defense mode. Battle animations could also be faster, but then everyone says that ;) I'm also fighting an awful number of bearded women, which feels like a bug, but doesn't overly bother me. I'd love to see a dungeon level editor come out, because I want to play with all the art assets :P I'd like to be able to save mid-dungeon (the mystery dungeon often ends up sitting in the background while I go to do other things), but I can understand that could be a pain. Basically I love this series, ignore all the haters in the comments, and keep making games :D
Changes I liked: the increase in gaining skill points, the new defense mode, the ability to get crafting skill through finishing dungeons, the ability to gain crafting skill through 'experimenting' with incorrect recipes, it being a bit easier to get the achievements in this version. Changes I didn't like: taking away the house to decorate, removing the ability to buy crafting ingredients, taking away the ability to see what the different buffs do. I didn't really mind that the bonuses from the achievements in the previous version were kinda weak, if they were too strong it would make the start of the game very boring.