Check out the best warlock guides for Vanilla / Classic WoW. Read our warlock guides for leveling 1-60, PVE or PVP guides and you will find a lot of tips to get the best warlock possible in Classic WoW.
The Demonist’s performance (like the hunter) during his leveling 1-60 is surely one of the most impressive. Easy and fast, the warlock shine in PvE solo.
In dungeons / raids lvl 60, it is a real support that brings damage and control. The Healthstone and the imp’s can bring important bonus in complicated situations.
Regarding PvP, the warlock is also very comfortable out of "instanced" fights. In future phases, when Blizzard will sets up the BGs, behind a melee first line, you can control the opponents with the Fear spell while your DoTs do the rest, awesome moment.