osu!'s score system has been broken since it's creation.
Score should be calculated using accuracy as a multiplier (thus making every hit worth the same). Actually score is worth shit since all that matters is how you do during the last part of the map since that's what's really worth a lot.
Factor used on score calculation should be accuracy and combo imo. Making the last hits worth more than the rest is stupid.
Then again Half-Time is completely imbalanced. This can be seen in every extremely hard map, where pro's cant beat Half Timers by playing nomod (or they just have a hard time doing it) which is, in my opinion, completely retarded.
After this you got Easy mod which is broken since it actually makes the map harder for almost everyone (how many people can play fluently insane maps + easy?).
Then the HR / HD discussion, both mods giving the same bonus. HR being a damn hard mod, since on insane maps you get AR 10, an OD close to 10 and a smaller circle size, meaning you need to have very good reflexes, a damn good accuracy since OD turns from being damn easy (like 7) to almost 10 which is really hard, and your aim needs to be way better (plus distance from hit to hit is increased a little by this). While Hidden just makes a visual change where snapping gets a little harder, and all you need to do is remember a few random hits that are hard to see using this mod. Only way this balances out nowadays is that most HR players can, for DAMN obvious reasons, do HR HD (there may be a few exceptions), but it still dumb that HR alone gives a lower bonus than another mod which requires you to be way better to FC. And remember, even if you're very good, getting 98% on HR is harder than getting 98% on HD, because of OD.
And on the last corner you got the competition between FL and DT, both mods giving the same bonus, but requiring completely different skills. FL being possible for every map if you play it enough times (it's just logic, play any map you can FC no mod for 2 weeks several hours a day, you will eventually FL FC) and DT requiring in many cases insane (many times impossible) skills to get the FC. Still many maps on DT are stupidly easy and FL requires a big amount of time to master/FC any map. So what should be done here is to change DT completely. DT bonus should be based on the base AR the map has (AR 9 DTs are just too hard for almost EVERYONE, even if the map itself is easy) and the base BPM of the map. Why the BPM thing? Many insane low BPM maps are just too easy, even using DT (example: http://osu.ppy.sh/s/30237), and those are cases where FL should be rewarded higher than DT.
But wait! There are some cases where low BPM maps are impossible on DT, if there was some accurate star rating system to see how hard each map is, I'd say to base DT scores on both BPM and difficulty (a very hard map should be rewarded A LOT MORE@DT than @FL).
tl;dr: Everything should be reworked/checked.
Score should be calculated using accuracy as a multiplier (thus making every hit worth the same). Actually score is worth shit since all that matters is how you do during the last part of the map since that's what's really worth a lot.
Factor used on score calculation should be accuracy and combo imo. Making the last hits worth more than the rest is stupid.
Then again Half-Time is completely imbalanced. This can be seen in every extremely hard map, where pro's cant beat Half Timers by playing nomod (or they just have a hard time doing it) which is, in my opinion, completely retarded.
After this you got Easy mod which is broken since it actually makes the map harder for almost everyone (how many people can play fluently insane maps + easy?).
Then the HR / HD discussion, both mods giving the same bonus. HR being a damn hard mod, since on insane maps you get AR 10, an OD close to 10 and a smaller circle size, meaning you need to have very good reflexes, a damn good accuracy since OD turns from being damn easy (like 7) to almost 10 which is really hard, and your aim needs to be way better (plus distance from hit to hit is increased a little by this). While Hidden just makes a visual change where snapping gets a little harder, and all you need to do is remember a few random hits that are hard to see using this mod. Only way this balances out nowadays is that most HR players can, for DAMN obvious reasons, do HR HD (there may be a few exceptions), but it still dumb that HR alone gives a lower bonus than another mod which requires you to be way better to FC. And remember, even if you're very good, getting 98% on HR is harder than getting 98% on HD, because of OD.
And on the last corner you got the competition between FL and DT, both mods giving the same bonus, but requiring completely different skills. FL being possible for every map if you play it enough times (it's just logic, play any map you can FC no mod for 2 weeks several hours a day, you will eventually FL FC) and DT requiring in many cases insane (many times impossible) skills to get the FC. Still many maps on DT are stupidly easy and FL requires a big amount of time to master/FC any map. So what should be done here is to change DT completely. DT bonus should be based on the base AR the map has (AR 9 DTs are just too hard for almost EVERYONE, even if the map itself is easy) and the base BPM of the map. Why the BPM thing? Many insane low BPM maps are just too easy, even using DT (example: http://osu.ppy.sh/s/30237), and those are cases where FL should be rewarded higher than DT.
But wait! There are some cases where low BPM maps are impossible on DT, if there was some accurate star rating system to see how hard each map is, I'd say to base DT scores on both BPM and difficulty (a very hard map should be rewarded A LOT MORE@DT than @FL).
tl;dr: Everything should be reworked/checked.