Cool review! Tower Madness is definitely one of my favorite tower defense games. One thing that this games does that is really unique that you didn't mention is that any player can view full replays of the top players' games on the leaderboard. So if you are ever stuck or want to get ideas on strategy or improving your score...these are like instant, real-time tutorials.
Also, the add on maps come in both open field and fixed path so fans of either type of map have something they will really like.
You are definitely right though, this is one of the few games where I absolutely don't mind not having any background music because there are so many sound effects going off.