The older modules won't completely crash on you, but there's a few minor changes in the way some scripts fire that may cause some modules to not function the way their designers intended. Without getting too technical, a recent patch (1.21?) changed the way the game engine handles creatures in different areas (to improve performance). One side effect was that some conversations that used to start when a player entered an area no longer start. Not every module used this particular technique, so many old modules are still playable. There are easy fixes to this issue, but they require the builder to go through and fix every affected conversation. Since this particular patch came out after MotB, most updated modules also require at least MotB. When in doubt, just glance at the comments, and check for a recent comment that confirms that the module is still playable.
Above all, just try to find a module that suits you, even if it's 3 years old and has mediocre score. "Goblins of the D-something Route", for example, I remember was pretty good even if it wasn't as massive as something like Dark Waters.