The first also had a mind-blowingly awesome and cool premise/devices, but didn't explore that concept's full potential.
The second just had an excessive amount of slow-motion action sequences.
That being said, I (who mostly watches current Hollywood flicks) found it refreshing to see no actors or actresses I had seen before, which sorta gave the movie's characters more depth as I didn't associate any actor/actress with the kind of role they usually have.
Beyond that, though the movie's storytelling could've been smoother, the main character's gaze more focused, and the ending a bit less predictable and therefore convenient.
Regarding the time travel itself, the suspension of belief required was a little too high. Moving in time AND space? No one around you reacting to your inexplicable clothes change? Physical contact with the device needed but only to a point? The list goes on.