As Dr. Gordon Freeman, you were last seen exiting City 17 with Alyx Vance as the Citadel erupted amidst a storm of unknown proportions. In Episode Two, you must battle and race against Combine forces as you traverse the White Forest to deliver a crucial information packet stolen from the Citadel to an enclave of fellow resistance scientists.
A necessary expansion with various engine improvements and a ton of mods available. Surprisingly, this game has better graphics than lots of mainstream crap today, at least on NVIDIA cards with SSAO and supersampling enabled. This is why HL2 E2 has so many modifications.