I have had mixed experience. Some DMs, myself included, want your game to be more like there's and make side comments to that effect (I try to restrain myself as best I can). Here are a couple of good things and bad things I've noticed.
Good.
1. DMs are well prepared, they know what their characters can do, and are usually ready to play immediately.
2. DMs are able to get into a really different character from their own personality, they are skilled at doing this from playing so many NPCs.
3. DMs are usually team players, they know the frustrations of a lone wolf character, and so make characters that are primed for group adventures.
4. DMs often make complex and fun characters.
5. DMs usually appreciate cool story elements.
Bad:
1. DMs sometimes are critical of the game, in the game. That can be very irritating.
2. DMs often consider themselves the Pro from Dover and can bully the other players. Especially if the other players see that person as a DM.
3. DMs can meta-game too much (I had a player who DM'd constantly say things like "the DM clearly wants us to be here, so look for clues.") That can be annoying as it breaks down the veil of disbelief.
4. DMs like to show off their knowledge of esoteric rules and loop-holes. Sometimes they do things in your game that they would never allow in their own games.
5. DMs can challenge their DMs in unintentional ways (Do you know about the Rule on AOOS?, Did you see the errata on that?)
Ugly:
1. DMs can make game breaking characters. Interesting ideas for an NPC might ruin games as PCs. Their rule knowledge and sub-conscious desires can combine to make them into a Frakenstein.
2. DMs can steal your players! I've been guilty of this one myself. I've joine dgames expressly for the purpose of scoping out some new meat. This by itself is not as bad as it might seem, after all they might want you the DM for their next game, and that can be a nive break.
3. DMs might know more than you. They might be able to pull the rabbit out of the hat with a little used spell, or unepected rule call. (Pyrotechnics used to allows get me).
4. Some DMs may take out aggressions on your players. If you run a group that is usually run by someone else, don't be too surprised if the regular DM decides to play a traitorous character, especially if it is one shot game. Good DMs usually don't like TPKs but as players in someone else's game they might actually enjoy back stabbing their buddies (especially if they have some pent up aggression).
I think some of the player-ability has to do with the playing experiences they've had. If they have been in good games as players, they will probably be good players. But if they have only been in crappy games (and decide to DM for that reason) you can't really know what to expect.
I used to always DM, I am happy to play though. I'd like to think that I am good player and DM, but I don't know if you can really judge whether you are a good player yourself.