Portability: Are you going to be taking your playpen to other houses? Perhaps you might want to spend a day at the park, where a playpen would be a handy way to keep your baby safe and let them play alone while you read a book? If you think you might be taking your playpen outside of the home, be sure to choose one that can fold up for easy transport.
Some models provide storage for toys and other baby items in zippered side pockets, fabric shelves, hook-on fabric storage pouches, and small clip-on parent-organizer bags. Of course those features aren't necessary, but if you want to use them, look for storage that is big enough to actually hold something. Storage compartments should attach, or be built into the outside of the play yard, so they're out of your baby's reach. One deluxe example is the S1 by Safety 1st Satellite Premier Playard - Pegasus (about $128), which comes with attached shelves and a small laundry hamper.
Nice to keep baby out of trouble at home. Once he became mobile we had to do an "upgrade" as we noticed he was starting to hit his head on the X shaped metal bars. We tried some alternatives but the best so far was wrapping the metal bars with pool noodles (see picture). You'll need 8 pool noodles and some cuts (buy some extra in case you mess up). Use 2/3 of a pool noodle to wrap the internal bars and the remaining 1/3 to wrap half of the external bar. The pieces will also need a longitudinal cut along the length to fit the bar in. You'll also need some small cuts in the middle of the longer piece to fit the center rivet, where the mesh is attached to the bars. We got the pool noodles at the dollar store nearby for less than $10 and since ... full review