In my humble opinion, the 5200 is a great machine to collect and play for even with its big shortcomings. I personally dislike the controller, but have to admit that with certain games, it is a BLAST to play with the twin stick holder(space dungeon, robotron). I was very lucky to score a masterplay interface controller, as well as have several 3rd party controllers that bypass the original controller. Also, using the trackball to play trackball compatible games on the system is awesome. Another plus about the system is the ultra clear signal that I have often gotten on several of the systems that I have owned over the years. For RF output, it is one of the best(sorry if not spoken technically)
The bottom line is that if you can look past the controller you will find that there are enough exclusives about the system that will totally make it worth collecting for.
If the controller thing really, really bugs you, then you can always settle with an Atari 800XL and get to play some crossover titles plus hundreds of more titles.