There's not enough words to really describe my deep love (and hate, but read on) for this game and I truly believe Oldschool RuneScape is one of the best games of all time. Right now is the absolute BEST time to jump in for the first time, or again after awhile if you've played before - this is the game's platinum age and you can't miss it. Steam charts do NOT grasp the full extent of the hype - 150,000 people play daily.

Here's my HONEST review as a veteran player. (TL;DR at the bottom)

In 2012, the developing company Jagex absolutely fumbled the bag and destroyed the original game (RuneScape/RS3) with a terrible-at-the-time update (too much to get into here), 6 months later in February 2013 after massive community backlash, they re-launched the 2007 version, the ''golden age'' of the game, and It went through a period of hype, quick die-off, long stagnation, and then re-development to create what is the game we all know and love today.

The issues that led to the downfall of the original cannot exist because all major updates outside of balancing require a successful vote via in-game poll system to pass (70%+) and these days the development team is comprised of tenured, veteran employees, and newer, dedicated, ACTUAL PLAYERS who've been through the lows of the past that now get to work on their passion and preserve it.

Every level you achieve, and every item you earn mean something. This isn't like many other MMOs you may have played where every new major content expansion or update completely nullifies previously sought items. Your achievements and effort mean something and will always stay. Your best-in-slot equipment, weapons, and armor do not suddenly become worthless upon an update. They may, rarely, be superseded by a newer item but the old one retains usefulness and value. The game thrives on it's horizontal progression system.

Instead of WASD movement, this game relies on your mouse and clicking the most. You'll still use your keyboard, but usually only your function (F1/F2 etc) keys to change UI tabs significantly faster than clicking the icon. Think of this as a rhythm game, all actions and functions are on a 100bpm/0.6s "tick" system. Focusing on the rhythm itself is ABSOLUTELY NOT ESSENTIAL in the beginning, and is only necessary at a late-game stage where select combat encounters and certain training methods require tick-precise input. By the time you get there, you'll understand. It's incredibly approachable from a know-nothing beginner standpoint, and easy to learn over time because the game will ease you into it.

Some people have a hard time enjoying the game due to the low graphics quality. I don't know what to tell people who are hung up on this. There are certain plugins on playable game clients that can resolve this to an extent - but I've always been a gameplay over graphics person. The low-poly style of OSRS is it's charm. You don't need "nostalgia glasses" to play the game, and I disregard that argument. This isn't supposed to be a modern game with modern frills, and if it's not for you, then it isn't for you - and that's fine.

The gameplay loop of skilling and killing can be rewarding for some, but a slog for others. I won't lie, it can be HARD to get into for new players if you aren't willing to make a commitment, but when you do it is extremely rewarding. The highest level per skill is 99. 50 isn't halfway, haha, no. It's 92 - because the experience curve is EXPONENTIAL. The original developers in 2001 never expected people to make it to 99, nor did they expect people to make a goal of getting 99 in *every* skill. Skills are, however, balanced well and 90% of playable content is unlocked by the time you're 1/4th to 99 (level 85), so maxing skills aren't strictly necessary but more of a long-term goal. For example, I've been playing OSRS since 2013, have significantly more hours off-Steam, and am still only at 2,330 total levels (maxed is 2,376) but enjoy all of the available content.

Finally, I can't speak to every issue the game has but I can speak two of the bigger ones, first, the 'bot' problem - it's not like TF2 if you're curious.
Like any MMO with an expansive game and active economy, there's people who want to make as much money (in-game, and REAL) as possible. Look up how reliant Venezuela is on OSRS gold. It's a big problem. Jagex is absolutely doing it's best to stop them and solve it, but this is an arms race as old as time, and cannot ever truly be won. I won't fault them fully for the issue, as it's only natural to be had, but they could be doing more.
Second, account security and customer support. For the longest time, Jagex has been notoriously HORRIBLE about keeping good customer support despite being a billion dollar company. They're recently been making public strides to improve this. Personally, I have not had issues. My infosec is good, but it isn't for everyone. Keep your stuff secure.

Most of the loudest voices talk about these two issues and while they are problems, they are not as massive and overblown as some people make them out to be - your mileage may vary.

So, with as much as I've written to be said so far, and without prolonging this review to the point nobody wants to read, I'll summarize with a quick TL;DR.

TL;DR, the game is fun. It's grindy, it takes time, and it has it's quirks - but if it wasn't enjoyable and rewarding it wouldn't be getting as much traction as it does today. Massive community, foundational in early internet culture and maintains a large footprint today. The phrase 'you don't quit, you just take a long break' comes from RS and is absolutely true.

Give it a try.