The Expendables 3 wasn't very good. First, the parts that worked. Mel Gibson was fantastic, as was Wesley Snipes. They both were clearly having a lot of fun. Harrison Ford is basically playing Bruce Willis' character from the first two movies, and he does fine. The rest... doesn't work. The four new, young members of the team are all bland, underdeveloped, and uninteresting. I get that they're trying to the concept beyond just the guys from the '80s, but they did it in the worst way possible. The two proper actors they chose were pretty sucky, and the other two are an MMA fighter and a boxer. Not exactly the best casting decisions when you're trying to make a new generation of action stars. They needed to be far more talented and charismatic, but it wouldn't have mattered because there are too many Expendables. Granted, Terry Crews gets shot and is in the hospital for most of the movie, but even minus him, there are nine Expendables, plus Ford, plus Jet Li and Arnold. There are too damn many characters in this damn movie. There isn't the space to develop anyone at all. That doesn't really matter with the old guys because we already more or less understand them because of their past work, but the new members are totally anonymous because they're unfamiliar actors. They need to have their characters developed, but there is no time spent doing so, despite the unnecessarily long running time.
Another issue is Stallone's character. After Terry Crews gets shot, Stallone decides to break up the team and gets Kelsey Grammar to help him recruit some young talent to go get Gibson because Stallone thinks that it may be a suicide mission and he doesn't want to get the rest of the veterans to die too. First, this goes against what happens in the second movie, which is basically driven by the team's desire to get revenge on Van Damme after he kills Liam Hemsworth. Very similar situation here, except this time Stallone tells the team to piss off and instead hires a new team who has no connection to the situation to help him instead, because I guess he prefers to get a bunch of twenty/thirty-somethings who are only in it for the money killed instead. Douche. (Oh, and only one of the new members gets any sort of motivation explained for why he joins up with Stallone.) This creates some irritating false tension because you know the old team isn't going to stay out of the movie for long, so you just end up sitting around waiting for something to go wrong and for them to show up to save the day, which they do.
The PG-13 rating isn't quite as intrusive as I expected, but it is definitely noticeable. Snipes and Statham both use knives, so the camera switches away quickly when they stab someone and it doesn't show blood, which really takes you out of the intended atmosphere, which is that of an old school R rated '80s action flick, but what is far more noticeable than the lesser amount of blood is the crappy CGI. The effects in the first two movies are, to my knowledge entirely practical with only one or two exceptions, namely the bit in the second movie where they fly the plane into the mine. In this one though, there are poorly CGIed planes, helicopters, and explosions on several occasions, and it is really annoying.
Finally, there is the really awkward "buddy dialogue," mostly between Stallone and Statham. This was in the first two also, but it was really bad here. It's hard to give examples, but you can tell when you hear it. Really stilted and unnatural dialogue that is supposed to be friendly banter, but just sounds really stupid. Hell, most of the dialogue sucks, except for a few bits here and there where it actually tries to be a bit more serious.
Overall, this was a really underwhelming followup. I liked the second movie a lot, but I was very hesitant when I first started seeing the pretty widespread negative reviews. Critics actually did seem to get what the deal is with these movies when the last one came out and thus gave it relatively decent reviews, so when this one started getting panned, I feared the worst, and I was unfortunately correct. If you liked the first two, I'm guessing you'll go see it anyway, but I recommend avoiding it. Go watch Lethal Weapon instead.