I've kinda come around to Cena the last few years. I still despise WWE for never allowing him to freshen up his character, but there's no denying that he is almost always in match of the night, despite everyone's opinions on him. You can't be involved in that many quality matches at such a consistency without contributing in some way. His moveset is familiar and unspectacular, but he plays his role very well.
The fact that he's actually losing cleanly every now and then is pretty nice too. I still firmly believe that an eventual 'Cena finally breaks' heel turn would be a beauty run to watch, but I don't believe that's ever happening at this point so what can you do.
Plus, it's hard to hate Reigns and Cena at the same time as I only have so much hate in me, so yeah. Maybe that was WWE's plan with Reigns all along to getting us to subconciously like Cena again.