I have also 'tried' to make Lysseos a favourite, having had it highly recommended by regulars that pre-date my firt visit to Plakis in the mid-90s, but I can't rave about it. The food is good, but always leaves me thinking that there was something that wasn't quite right.
Kleftiko is an old favourite of mine and while it was good, the local Greek resstaurant in the village that I used to live in in the UK made a better one. I like quite highly spiced food and perhaps this is where thing go wrong, for me at least. Not stupidly hot curries, but loads of flavour. But, given Kleftiko's origins perhaps this is how it really should taste.
I suspect that this is merely a case of my liking for Plakias leading to too-high expectations, but all the same... I could certainly recommend Lysseos, all the same, and given the lack of seating after 19:00, I doubt that I would need to.