Lille's isn't so bad except for the fact that Lille-Europe pretty much only has Eurostar and Lille-Flandres is most everything else. It's walkable but a bit announcing.
Most TGVs that don't go through Paris depart from Lille-Europe rather than Lille-Flandre though. Lille-Flandre is mostly for local (non-TGV) traffic and Lille-Paris as far as I know.
There's also a metro connection between the two (one station) that is accessible for the disabled (... or people with heavy luggage) and that is free if you have a valid train ticket although it's not advertised anywhere.
