Sorry, I missed this somehow until now... I didn't see Ant Man yet, but I did really like Guardians. When I say they've gotten stale I mostly mean the Avengers and all the individual movies that go with them. Thor, Thor 2, Captain American 1-3, Iron Man 1-3, Avengers 1 and 2... they're all blurring together to me. Especially the last few I've watched (Winter Soldier and Avengers 2). It seems like Hulk and Hawkeye and Black Widow just keep showing up to show up... the stories seem to be getting less exciting...
To each their own I guess. I grew up with a monthly sub to Avengers comics, so I'm sure I have a bias towards seeing these characters on the big screen. The first Iron Man and Avengers were amazing films IMO, so I can see where sequels to these might be a let down. Each of the first "individual" movies was an origin story, so I don't really see any of those as re-hashed with the sequels. Thor 2 felt a little more like the first Thor to me, but all of the others have been really different from my point of view...
- IM2 gets War Machine in on the act and they have to battle both Whiplash and HAMMER industries' Iron Man drones. Both are classic Iron Man baddies and they complemented each other versus being forced into the story like we've seen with Spiderman.
- IM3 has Tony building out a plethora of his own unique Iron Man suits (awesome to see in itself), but also did a great job adding some character to the story when he goes off the grid for a while, panicking about the new super hero life he's taken on. This a terrific lead in to Avengers 2 and why he even builds Ultron
- Cap2 has the boy scout betrayed by the government he's so loyal to, which is more great character building. The fight scenes in this one were amazing and it introduces a really great take on Falcon. Nice lead into Civil War as well
- Cap3 guessing you didn't really see this since it doesn't exist yet, but Civil War pits the heroes against each other, which is another really original concept. We see some earlier bickering among the heroes, but not as anything serious.
- Avengers 2 has a really unique villain in Ultron - being the first real baddie that the team needs to join together to beat. Two new characters and a surprise death, with almost the whole team turning over by the end.
- Ant-Man easily cleared my top 5 for Marvel movies and has a very different feel again with more of a redemption story than the others.
I guess I just don't see what's stale about any of these. The characters and storylines are meant to intertwine, so it feels like one really big story with a lot of fun chapters. I even read the comics these movies are mostly based off of and felt the stories were pretty original, but like I said earlier, maybe I'm just too much of a fanboy.