Demos aren't all that common anymore, but Deep Silver and 4A Games seem to want to change that. Metro Redux has now gotten playable demos for both Metro 2033 and Metro: Last Light. Although it's just for Playstation 4 and Xbox One, both demos are said to consist of one third of each game. That's a lot of gaming.
The demo versions can be found on Xbox Store and PSN, and if you happen to like them you can purchase the rest of Metro Redux and continue playing where you left off. The save games carry over, so you won't have to start over again.
If you still need a little nudge, you should check out our review from when the remastered games were first released.