The microline has some "theoretical" advantages, all else being equal. It contacts more of the grove area which should result in less record wear give you a slightly better signal-to noise ratio. And assuming it contacts a different part of the groove it might minimize the sound-damage done by previous record wear.
The main difference in "sound' with different cartridges is frequency response and that can be tweaked with tone controls or EQ. Also there are some "hard to track" records and a different cartridge may track better for less tracking distortion.
mtcm77 mentioned capacitors & resistors - The load on the cartridge also affects frequency response. Regular moving magnet cartridges are usually rated for 47k Ohms and some capacitance. Almost all phono preamps have the proper 47K input impedance so the resistance shouldn't be a problem. Usually the ideal load capacitance is listed in the cartridge manufacturer's specs, but
the actual capacitance load is usually unknown because it's a combination of the phono preamp's input capacitance, the capacitance of the connecting cables, and the capacitance of the wiring inside the turntable. Sometimes you know the specs for the preamp, and some preamps have variable capacitance settings. Occasionally you can buy cables with a known capacitance (cable has a certain capacitance per-foot), but we almost never know the capacitance of the wiring inside the turntable.
...Usually it's just "plug and pray". There are LOTs of variables, including the records, so the best thing is usually to adjust the tone controls/EQ by ear. Or if you really want the BEST sound, toss the outdated-inferior technology and go digital!
