they're fine, but, being more complicated, do sometimes go wrong. Old simple ones have hardly any working parts or eleectronics.
the most common fault seems to be that the ducts in the back, where cold air is blown through, clog with excessive frost and get blocked with ice, more than the automatic defost can melt. Effect is that temperature is too warm. Remedy is do do a manual defrost until there is no more dripping (can take 24 hours)
if the cause was door being left open, it will probably not recur.
if cause is damaged door seals, renew them
if cause was automatic defrosters failing, may be uneconomic to repair.
IME new FFs are more economical on energy than old ones. They seem quiet.
Which reliability ratings (best first)
Fisher & Paykel 88% ★★★★★ 78% 91%
Haier 87% ★★★★★ 72% 91%
Samsung 86% ★★★★★ 73% 92%
Panasonic 85% ★★★★★ n/a 95%
LG 84% ★★★★★ 78% 98%
Bosch 83% ★★★★★ 69% 85%
www.which.co.uk/reviews/fridge-freezers/article/top-fridge-freezer-brands-anUP31D5GeNb - Which?