Hi Mariocyprus, perhaps the game 'Perfect World' may be what you are looking for? I know it has a lot of mobs, it's a free game and hs an item mall. You can upgrade your weaponry and armor and has a killer Auction House. The graphics could use some work, however I do believe you can solo kill bosses!
I wanted to give a link to a video I recently made, the game I'm playing is World of Warcraft and I'd love if I got feedback on it. ^.^
For a little description, it is a Mage PvP video which features Arenas, BGs, and WPvP in a seven minute long video. The video also contains added humor to it with Meme's and a Blooper at the end of the video. To see this video, copy and paste this link into the Browser. Enjoy!
http://www.WarcraftMovies.com/movieview.php?id=232587