Gurren Lagann was the first anime I watched as an enthusiast, and not just a kid watching Dragon Ball Z over his cornflakes. What an excellent place to start. In fact, I'd probably recommend it as one of the first anime to watch, if anybody is looking to enter the genre.
The English voice acting is of fantastic quality, the visuals are pleasing, the characters are loveable, and the action is great fun to watch. Despite not being a particular fan of the shounen genre, I did enjoy this a good deal, and have even rewatched it.
Gurren Lagann is an anime classic, and a must-see.