The ending (NO SPOILERS, PLEASE)

I have just watched the 1st episode of season 1. Trying to decide if I should watch the whole series.

Can someone tell me -- WITHOUT ANY SPOILERS, PLEASE -- if the series is wrapped up nicely by the end of season 4 (all plot-lines resolved), or does it end on a cliff-hanger? I'm not sure I want to invest in watching the whole show if it's going to be a frustrating end.

Thanks!