I just played the WAD, so I can share some feedback:
-The maps vary widely in quality from the early ones to the later ones. I'd guess that you created the maps in the order that you placed them in the game.
-I found none of the maps particularly compelling, for various reasons, which tend to be more noticable in the earlier maps:
-The difficulty was a bit low for modern standards, but that's your choice, and it fit well within Doom II's standards.
- Much of the gameplay was repetitive and uninspired, consisting of linear key/switch hunts and dull fights.
- Your texturing could use improvement. Specifically, there were three problems here: Many levels use only a single wall texture for huge sections of the map; some maps use the same floor and ceiling in almost every room; it looks terrible to change flats abruptly without changing the sector height or using borders -- Romero's widely quoted mapping rules mention this, but you should look those up for yourself.
- The architecture tends to be mostly square and uninteresting, and the earlier maps are very flat. This is improved in some maps and rooms, but it's still a big turnoff.
- Most of the maps consist of numerous narrow hallways linking a bunch of rooms, which I personally think is an irritating design style.
- The final level felt extremely amateurish, with all the Cyberdemons. I think of the boss monsters as a stong seasoning, which should be used more sparingly.
So, while I had some fun playing them (it's pretty hard to not have fun while playing Doom :P ), I think you could definitely do better. Of course, taking into account that this is your first project, I'd say that it's nicer than many early attempts, and I look forward to see some more (improved) mapping from you.
(Also, I wouldn't exactly call MegaUpload an 'FTP site')