Opinions will vary. Both are superb in different ways so it comes to what is more appealing to you. The dark atmosphere of Metro or the lush grassy urban jungle of Crysis.
With that said I will say this. Metro 2033 was horribly optimized and it is a good chance that Last Light will be as well. Im excited for Last Light though. my friend is extremely excited for it and sends me videos all the time lol