The Warlock class information is on page 31 of the "Playtest 5" document linked at the top. You do indeed get only ONE of the pact cantrips. Warlock is also a half caster, with spell slot progression similar to Paladin or Ranger. Mystic Arcanum is an invocation rather than a class feature, and may be taken multiple times to obtain access to spells higher than level 5 (where warlock progression tops out). Spell slots regenerate on long rest now, rather than short rest.
I can understand why they would make this change. Warlock was always the odd one out when it came to multiclassing spell casters, and turning them officially into a half caster will make that easier. Still, I liked the short rest spell slot refresh, so I don't like this change.
The blade pact cantrip specifically disallows heavy weapons, which means that it misses out on the best part of the great weapon master feat. It also applies to melee weapons only, but thrown weapons are allowed. So... not clear whether sharpshooter will work. Great Weapon Master and Sharpshooter also do not appear in either the playtest 5 or playtest 6 document, so its not clear whether or not they will still exist in their current form.
Lifedrinker moves to level 9, but gives a D6 instead of cha mod damage. It also heals the warlock the first time it is applied during a turn. This is basically a small nerf, but I suppose its not too big a deal, and getting it at 9th is nice. I think that the lack of heavy weapons is a bigger nerf. Hopefully they change that.
