I'm currently Rank 19, what's so bad about the base game? Is it the lack of overall mission types (Job, Mission, Deathmatch, Race, Parachute, and Survival)? Jobs and Missions do offer more variety than the others, but that's probably why it's super easy to get a full lobby for them and a nightmare to get certain races and deathmatches going. Especially races, if you want to unlock specific vehicle class upgrades.
It may be because I'm playing with a really small group of friends instead of full games (full of the type of online gamers that I hate in other games) but every time we play it feels like we're going through the motions, trying to unlock all of the things for free roam that Rockstar locked away from us.
I can't believe I'm saying this but we all agreed tonight we had way more fun with GTA 4's free roam despite that game having almost nothing to do in the free roam. Maybe it's because it was the first of its kind and now, 5 years later, it's not impressive anymore. I still think it's because Rockstar F2P'd all of the design decisions in this game and it drastically hurts the fun.
Everything feels like it was purposely designed to make sure you're not having fun. Got a fast car? Can't keep it, need to buy one for a ridiculous amount of money. Want to mod any car? Besides unlocking it all you need to pay like $10k+ to do it. Got a tank? It dies faster than most cars. Got a sweet jet or heli? Same as the tank, bounce it off the ground or a tree once and the heli will be smoking already. Want to do anything fun but semi-dangerous with your friends? Tough to do since you die almost immediately from anything in the game. I don't even know what body armor is for when you lose it in 2 bullets, even with the 75% armor which is what I have unlocked now (I'm level 31).
What really made us just lose hope in this game was Rockstar taking out the ability to launch almost anything with helicopter blades. I jumped from a roof on to my buddy's hovering heli and I just...died. In GTA 4 I would have been launched halfway across the map. That was like the disheartening straw that finally broke my back after experiencing all this other stuff.