There is always a risk with these 'period' pieces that it will become dated very easily with changing tastes & expectations. Fortunately, caper movies are still getting made ('Entrapment'), Redford is still a sex-symbol, & crime still pays. So 'Hot Rock' is as eminently watchable today as it was way back then, provided of course you don't start wondering too much about the plot. Ride Quincy Jones' music (Gerry Mulligan plays the sax) & Redford's easy charm & you are safe home.
The performances all round are very muted, except the wonderful Zero Mostel's over-the-top crooked lawyer. At times you feel everybody is just too reluctant to get on with it, but I guess that is the kind of 'cool seventies' effect that director Yates was trying to get (& I feel, succeeded). Anyway Yates was riding high at this time with some great movies like Bullitt & Murphy's War & his confidence shows.