I've neither seen the movie or any of the ads/trailers/spoilers etc.
If we go by TV models such as "Revolution", the answer would be that it would take quite a while before we returned to a civilization as we know it.
However, there are other schools of thought (In the Sci-Fi world) that a new or fresh start on a distant planet would only encourage the rapid development of civilization as well as exceeding our previous understanding of it.
Plenty of things would be fairly obvious if you looked close enough. Incongruous chemical signatures would be everywhere in the soil and to a lesser extent the air, and it would be pretty hard to explain the distribution of certain species without us as the vector (eg: the presence of rats and dogs or specific European species on remote Pacific islands)
There would be a few really obvious artefacts that were there to be found. In the US the monument Mount Rushmore is expected to last for many tens of thousands of years. It's in a fairly stable bit of geology and it's cut into granite, which is seriously hard. Should be there for any alien archaeologists even if we're long gone.
The longest lasting proof of our existence won't be on Earth though. The artefacts from the Apollo missions on the moon could well last for millions of years. Galvanic corrosion will eventually break down the technological components, but that could take a very, very long time. The moon isn't particularly geologically active, so the astronauts' footprints will stay exactly the same until something disturbs them, which might not be for many millions of years.
The pyramids and other surviving megalithic constructions like that are also built with less of the dynamic tensions that decay could release. They're basically stacked on the ground. You couldn't well build a skyscraper out of stone, and a Great Pyramid made of reinforced concrete might outlast the original (although weathering would be a serious issue.) The fault tolerances when every square cm of ground is load-bearing seem rather higher. = )Stone may be a poor building material in a lot of ways but it is just more stable than reinforced concrete.
I know I shouldn't use tildes for decoration, but they always make me feel at home~
The film in question seems to have been panned by some critics. The audience seems split too. I'll wait till it arrives via my satellite dish or aerial.
On the question, the earth will return to being green and blue with fantastic views of the cosmos due to no artificial light.
A concrete pyramid wouldn't do as well as the real ones, concrete just insn't as stable chemically, and corrosion of the rebars would cause spalling. Not that you need rebars in a pyramid, you'd be better off using unreinforced concrete.
The Colosseum is made of concrete IIRC, so it can last a few centuries in reasonable shape.
I guess the gold record on the Voyager probes could last a long, long time though. Gold is super-stable, so that should last until it falls into a gravity well and gets swallowed. That could be a really long time.