I'll talk about sidequests, and other things in the future, but for now I'll discuss the current bit of the game I'm spending a solid chunk of time playing, the SIVA Crisis Heroic Strikes.
Strikes in Destiny are 3 person encounters, where you'll (usually) be matchmade with two other players, or you can play with people you know, where the aim is to get to the boss through essentially wave of enemies, and then defeat the boss.
There are a whole bunch of these activities that have been put together in a playlist, and the playlist is always on random.
Where does the grind come in? Well, your character has a light level which is an average of all of your pieces of gear, of which there are 9, and you can only incrementally raise it. The pieces that drop at the end of the heroic strikes will be one to two light levels higher, and will drop 2 to 3 pieces of gear. That's great and all, but pieces like ghosts and artifacts don't drop commonly and are frequently the source of frustration, being the limiting factor in progressing. This means that if you're lucky and you sequentially get new pieces of gear in order you can increase your light level by one reliably every 3 strikes, which will take roughly an hour.
But it rarely is sequential, and with one bit lagging behind and no progress in that area for a while and you could have all but one slots having the same light level, and you've hit a cap until you get one piece of gear that will assist you in your search.
The game isn't particularly slow on the grind, but the grind at this stage is going from 340 light to 365 light, and that's a lot of hours. Luckily there have been things along the way that help out, like vendor gear being purchasable at 350 light, and drops from factions being provided to assist you in the light level climb by being awarded at above your level, again for a random inventory slot.
I hit 360 light today and I'm feeling good, the total cap is 385, and I'm a way off of that, and as soon as the hard raid is released, all the caps change, so the end strike blue drops will increase in light, the legendary drops will be higher and the grind changes in complexity again.
Have an excellent day! You're all my favourites!