I'm currently level 16, and am "blocked" on the story. You have to do four trials which are basically collections of achievements. Kill 50 enemies with melee, etc. You can complete these achievements in the earlier story missions, but it's likely you'll be missing a few of them, so you have to head into FreePlay for a bit.
The major problem for me is that one achievement (open 15 chests) was bugged, and it only counted if you were the person to open the chest. It has since been fixed so that it counts if anyone opens a chest near you. But I entered FreePlay with zero chests, and have been slowly accumulating more. Most of the other achievements were about 80% complete, except Ultimate Kills. Apparently I wasn't using Ultimates earlier in the game. But since they're Ultimates, you rack up kills with them quite quickly.
FreePlay is a bit lonely. The map is very big, so meeting up with other people already in the map is rather time-consuming. As well, people leave and join often. You meet up with someone, do an event, and then they leave FreePlay and you have to go find someone else. You don't see World Events on the map, so there's no obvious location where people converge.
Once you meet up, wandering with people and doing events is fun. I guess if you played with friends, or an online community, it would be even better. Note that you don't have to group up. You can do most things solo, even the events. The only thing I was unable to do by myself was kill an Ash Titan. So much fire!
Javelin-wise, I've unlocked the Ranger, Colossus, and Interceptor. I don't care for the Interceptor play-style. It is a fast, fragile, melee type, which is just a bad fit for me personally. However, I really like the Colossus.
The Colossus has a shield, and you can hold up the shield and then charge at people, dealing damage to them. I have a component which increases that shield damage by 300%, so my Colossus just runs around the battlefield stomping mobs. It's pretty hilarious. It doesn't really work with flying enemies though.
In other news, I bought a Logitech g600 mouse for use with Anthem. Somewhat ironic, since it is an MMO mouse. But I found I needed about 4 extra buttons, and they were awkward to use on the keyboard. So far the new mouse is working well.
Anyways, I'm still enjoying Anthem. Hopefully I will get past this stage soon and then back to the story.