He was fairly decent, then went to Swansea, then dropped to League One to play at Fleetwood at the age of 26 making 23 appearances in 20/21. Returned to Scotland to Hearts where he was back in regular first team football, which is a decent reminder of the level of the Scottish Premiershipleague.
Forest fans seem to have a blindspot for mediocre wingers who can run a bit but actually produce little threat or value. Barrie McKay and Garath McCleary were both shit from the outset but a large part of the fanbase were determined to manifest them into the next coming of Gary Crosby when they were both at best Temu Chris Allen.
McCleary clearly had it, right from the off. What he needed, unfortunately for us, was a couple of years adjustment to the physicality of the professional game (and to get the other side of the billies).
Barrie McKay was decent in his first few weeks but lost it quickly (probably defenders realised that they could get physical and he'd give up) and was no use after that. McCleary had a great two months at the end of the season when we stayed up under Cotterill/O'Driscoll (won PotS, as well) but did nothing outside of that for us and I'm not aware of him being brilliant at Reading subsequently.
I think that's slightly harsh. McCleary was no world-beater - I think we can all agree with that. But he played in the Premier League with Reading, who he also went on to play nearly 250 times for (presuming most of them at Championship level). That was after more than a century of appearances for Forest (and 13 goals).
He was a good level above Barrie McKay. Or maybe he was utterly useless, as you say, and somehow managed to con four clubs into allowing him in excess of 550 professional run-outs.