Galaxy Note 4, being launched in September/October 2014, is now about 3.5 years old, but being a flagship, it still performs pretty competitively even against many expensive and newer flagships in most aspects in real world usage.
Few major weakness I came across in my use.
1) Battery timings, due to fake batteries. Fake batteries hardly last 3-6 months and give bad timings (very big issue for me).
2) Camera is very good, but not great compared to latest flagships.
3) Stuck on Android Marshmallow. iPhone 4S, being 2011 flagship is on iOS 9.3.5, last update received a year ago.
4) Outdated design.
5) Rest everything is comparable against latest flagships. Not significantly inferior in any way, like overexaggerated in comparisons.
Using Galaxy Note 4 and Galaxy Note 8 simultaneously in 2018 made me realize that latest flagships are all hype and nothing too groundbreaking (RIP price to performance and true innovation). They are just hyped up small incremental refinements.
Other factors like processing power, display quality, build quality, user experience and other features are still comparable to latest flagships. Not significantly inferior in any way, like usually overexaggerated in comparisons.
But getting rid of Note 4 due to battery issues anyway.