Considering characters at the moment and one option is the Warlock. Looks pretty cool. Anyway, I notice Pact of the Blade, which immediately appealed, but the problem I'm having now is I can't see why I'd do that over and above spamming Eldritch Bolt?
I'm generally not very good at the build crafting, so I may be missing something, but there doesn't seem a way to enhance that summoned weapons damage beyond spreading your stats out to STR? While oddly, there is Eldritch Blasting enhancing options within the class.
So...is Pact of the Blade viable without multi-classing?
Viable but tricky. I spent a while tinkering with it the other day. You do get more damage output than a straight blaster; the blaster only gets to add her Charisma bonus to damage once per round, where you can add your Strength or Dexterity bonus twice (Thirsting Blade) and eventually layer Charisma on top of it (Lifedrinker). But you have some nasty weaknesses that take work to overcome.
The problem is you only get one pact weapon, and you are proficient with neither medium/heavy armor nor shields nor martial weapons. That puts obstacles in the way of any of the three standard approaches to melee. Only one pact weapon and no martial weapon proficiency means your two-weapon fighting is limited to a dagger in the off hand, and it doesn't get any of your pact weapon benefits. Lack of shield proficiency means you can't sword-and-board. And lack of proficiency with non-light armor means that focusing on Strength over Dexterity will cripple your AC, which is a major obstacle to using a great weapon. I generally think people overrate the importance of AC, but a dedicated melee warrior needs better than a 13.
The simplest solution to all this is to put your first level in a melee class: Fighter, paladin, or ranger. You get the proficiencies you're missing and you also get a fighting style to complement them. However, you want to be a straight warlock. We can do that too, just takes a bit more work. Keep in mind that you're building for melee, not spellcasting. Charisma is nice but your attack stat comes first.
Two Weapons: A couple of ways you could go here, but I would probably make this character a drow. Why? Because drow come with built-in rapier and shortsword proficiency. You can start with a 17 Dex/16 Cha, spend your first two feat slots pumping Dex to 20, and then pick up Dual Wielding at 12th level. For levels 1-11, fight with shortswords. At 12th level, replace them with rapiers. The two-weapon approach is my least favorite, frankly, because the off-hand weapon doesn't benefit from any of your abilities and because it eats up all your feat slots through 12th level. On the other hand, if you're playing in a campaign where feats aren't allowed, it's pretty much your only option. A two-weapon bladelock can get by without Dual Wielding, but great weapon and sword-and-board are both absolutely dependent on Moderately Armored.
Great Weapon: Play a human using the "+1 two stats, bonus feat, bonus skill" variant. Don't even consider any other race. That 1st-level feat slot is critical because it lets you get Moderately Armored right away. Start with 16 Str/16 Cha and use Moderately Armored to get your Str to 17. At level 4, get Heavily Armored to reach 18, and then at level 8 you can use a stat boost to reach 20. Your 12th-level slot can either boost your Charisma for +1 to damage via Lifedrinker, or it can go to Great Weapon Fighting. The latter is probably better.
Sword and Board: Again, play a human and grab Moderately Armored right away--in this case, for the shield proficiency. You can either pursue the same build as the Great Weapon bladelock, pumping Strength and using a longsword, or you can go the Dexterity route and fight with rapier and shield. I incline toward the latter, because Dex is so much more useful out of combat. Start with 16 Dex/16 Cha and use Moderately Armored to hit 17 Dex. Put your level 4 and 8 stat boosts in Dex, with the extra stat point going to raise Cha to 17. Then you can get Actor with your 12th-level feat, raising your Cha to 18 and allowing you to pull all kinds of shenanigans with Master of Many Faces. (I'm a huge fan of the Actor/MoMF combo. Not everything is about combat. If that doesn't appeal to you, though, you can do other things instead.)
There are other approaches you could take, but these seem most promising to me.
