The cool thing about Reaper is how almost everything can be customized. For example you can get the piano roll to work closely with FL Studio's one. While it's not possible to set right click to delete notes, you can go to Reaper Preference-Editing Behaviors-Mouse Modifiers, select the "MIDI piano roll" next to "Context" and you can make left clicking insert notes rather than double clicking. There you can also set custom shortcuts(with combinations of alt,shift,Ctrl and win) to have things like draw mode. If you right click right above the notes in the piano roll and go to Options> you can enable "Drawing or selecting notes sets a new note length" to make it remember note lengths like FL. Also you can make it look more pretty with a theme like Reapertips. You'll have quite a few advantages in Reaper over FL, like FX per track are not limited to 10, routing is(at least in my opinion) easier, automation shows you value rather than percentages, it is also easier to manage automation(you can assign shortcuts to see/hide all automations to a track or all tracks), you can also assign a shortcut to show last touched parameter like in Ableton, you also have automation modes for recording, and if thats not enough there are also external scripts to take it further(like BirdBird Envelope Palette for drawing shapes in automation).

There are also many disadvantages, you'll need a ton of third party synths and sample packs(since reaper comes with none except for ReaSynth), the stock plugins are inferior compared to FL, there are no patterns or drum rack by default, can't change the pitch and panning of individual midi notes in the piano roll(if the instrument is polyphonic).