The tiles are nice, but there is very little variation (at least, so far). When making a level/area/stage/whatever, keep in mind that you want the player to enjoy going through it, looking at it, wanting to check out what comes next. If you treat it more like an obstacle for the player to get through, it will likely turn out rather uninteresting. Usually games tend to have moving things as a main method of keeping the eyes entertained, making the game feel more alive. It's incredible how much difference animated things make. Also graphical effects like: particles (e.g. sparkles, dirt pieces, smoke/dust), glowing effects, sun ray overlays, reflections in water, etc., can all make a fairly minimal tileset look a lot better, which makes the game more interesting to play and much more enjoyable and memorable for the player.
Always be thinking of ways to make your game stand out amongst the crowd. Make it memorable. I really like your pixel art style for the most part. The biggest flaw I see in it is the font, which looks a bit sloppy; it should be more uniform. Just look at the lower case "m" and "n" against the lower case "e" to see what I mean. The problem with it is that it makes it hard to read, and the MOST important thing about text is that it should be easily readable, because that is it's purpose, to be read.
Besides that, the bar with the star on it has the black outline border run through the star's black outline, causing - for lack of a better word - "interference", which screws up the star's definition (I hope you follow; I probably could've worded it better). It might be better to simply make the star BE the end of the bar, rather than having the bar come under it. It would make things cleaner and more defined. Actually, now that I look at it, the 1's outline is having the same problem. Not to mention that it also takes away the "curve" to the bar's edges. You might want to make that bar thicker as well, or at least make a design that has the part with the number thicker, so it doesn't have the same problems.
If you fixed those things, I would love this completely. I am especially loving the tiles, the character, and the character's mug. Very nice work! I hope I helped you a little. I'm always looking to help fellow aspiring game developers.
EDIT:
I saw this and realized you probably already have a good grasp on level design:
http://tamerkoh.deviantart.com/art/World-of-Chaos-2-Graphical-Style-345849885Aw well, maybe I helped you a little bit anyway.