[D&D 5] Are Monks good front-line brawlers?

I will (hopefully) be playing in a DnDV campaign soonish with three other players and so I have been thinking about to play.

I must say that from reading the PH the monk looks pretty good but I want to know for people that have actually played as them:

Are they viable front line brawlers or do they work better as in a harasser/hit and run specialist?

I feel like a party of four can't afford to have a weak front line so I just want to make sure that I won't be screwing my party by picking a monk.