The first level: I've seen worst
outside levels: Not bad
first level the custom graphics just delete them they really look bad.
Outside I didnt look to closly for errors but one thing stood out at me is the stairs they look messed up might want to fix them.
All in all you have quite a bit of potential. Currently you're skilled enough to have a decent chance at getting a job as lat some where assuming you dont already have one.
One thing I really liked is how your levels dont look super cluttered and hard to walk through.