The only thing the game needs is a resizable graphics update. When you first start playing you're going to have a hell of a lot of difficulty adjusting to the tiny ass screen; not only because you're used to HD, Fullscreen RS but also because your computer monitor is probably higher resolution than it was in 2007 - making the client appear even smaller on the screen.
If you can get past that, and you do after a couple of days, its a far better game than RS3 is in terms of feeling purposeful and streamlined. There's none of this bloat that RS3 has, stuff is worth like 10x more in terms of effort required; which is nice, things in RS3 have become pretty meaningless. Runescape is a grindfest and when you grind in OSRS you feel like you know why you're doing it and you know that when you achieve a 99 its actually going to be an achievement.
Yes, play OSRS, especially if you played runescape in the early days - the community is much better and if I'm honest, the smaller dev team is far better at PR.
I think that a big part of it for me is going to be ruined by the trading post though, which is a shame.