I thought we pulled out of Afghanistan and then went back?
I wouldn't criticize it, except for we had no reason to get involved. They aren't our responsibility. Also, in addition to doing our own stuff and supplying our own equipment for Libya, we also were supplying aid to the civilians. There were A LOT of tomahawk missiles in the airstrike on Libya, and those aren't cheap. Fox reported the cost at ~600,000, but the more liberal news stations reported them at over a million apiece. We were already in debt when these things started happening. All this didn't help. Is it being relatively cheaper an adequate justification for doing it over and over?
He kept talking about bringing troops home, but really they're all just being relocated. And wasn't doing air strikes on Libya technically something he should have had permission for? If I remember right, he never got it, which set a precedent for future presidents to start 'skirmishes' without Congress or anyone else involved. Those can escalate into full-blown wars at any time. Sure, he's picked countries that aren't exactly going to come at us, but who's to stop someone in the future from doing it now that now they know they can do little war actions without permission.
Edit: That was already answered.
George Bush increased troop numbers before he left office and that plan continued after Obama was elected because the surge policy required it but in the last year they started the process for (I think) over 30,000 troops to start to withdraw from Afghanistan so the numbers are definitely going down now.
As for Libya, while not the official responsibility of America (or NATO) they clearly felt that they had a moral responsibility to protect millions of innocent civilians from being murdered solely for wanting democracy in their country. In total America probably invested less than half of the total spent on Libya despite having a military budget many times that of the rest of the NATO countries combined so it was negligible really compared with the amount of lives saved. I guess opinion on that would depend on your individual opinion on the worth of a human life regardless of their nationality.
In terms of permission, they had a UN resolution to enforce a no-fly zone and to protect civilians from attacks by the Libyan government.