Welcome to Planet Hyatt
I've stayed at this Hyatt many times over the last 5 years. It's not my hotel of choice in Chicago, but sometimes it's the cheapest and it's also connected to the Pedway, which is convenient during winter months. The hotel itself is really two separate (but connected) towers. It really is a huge space, so be prepared to walk, especially after check in if you're in the east tower. 
The rooms have improved in recent years due to pretty aggresive upgrading and rehab. The "Junior Suite" was by far the best experience I've ever had at Planet Hyatt. The room was spacious, clean, well decorated and had an amazing view of Chicago, though the bathroom was very small - smaller than the bathroom in a standard room which was pretty confusing. On a separate trip I stayed in a standard room, which was...standard (I would have angled for an upgrade, but the lady checking in beside me was expressing her outrage to the poor staff about her lack of upgrade, so I thought I'd do them a favor by keeping my mouth shut and just accept the room I actually paid for). Also clean, comfortable and totally sufficient. 
The hotel overall lacks a personal feel. There always seems to be a pretty big mix of business travelers, tourists and conference attendees (if you do stay here get ready to laugh at the pretty random conferences they hold). That said, the staff I have interacted with over the years has always been friendly. By far the largest annoyance is the Internet fee. $9.99 per night is the standard rate, but they offer an upgrade to a faster speed for several dollars more. Another small annoyance is the prevelance of connected rooms...there's nothing worse than hearing your neighbors when you're trying to get to bed early, so make it your mission to find a room that isn't connected to another!
I'll stay here again. I'll roll my eyes when I book it because it's not my first choice. Then I'll arrive and realize it wasn't so bad afterall.