Depending on your suspension setup, mine isn't too bad. If you have a DCC, Comfort mode with the current setup (19" wheels and lowering springs) feels like a Sport mode when everything was OEM. With 18" wheels (just lowering springs), Comfort mode with the current setup felt like a Normal mode, and Normal mode felt like a Sport mode.
I bought Englishtowns because I love the way they look on a GLI. They come standard with 235/35/R19 with the Golf Rs, but I've found they are too stretched, that's why I bought 245/35 which is better for the ride quality and has more grip.
My Eibachs are for the MK7 Golf R instead of GLI because I wanted to keep the ride quality closer to OEM as much as possible. They are one of the few aftermarket linear springs available (this is important if you have DCC shocks, they don't like progressive springs). They are very comfortable for an aftermarket spring, almost as good as OEM. The rear springs are stiffer than the front, which is the ideal setup for a FWD car. GLI-specific aftermarket springs usually slam the car with tons of reverse rake, which I hate the looks. I measured the gap, and all wheels have the exact 13.75" distance from the center of the hub to the fender/quarter panels.
Long story short, the ride quality isn't harsh, but you will definitely feel that it is firmer. You still need to be careful with the big potholes though, lowering springs is not the optimal solution, no matter how good they are. If you have the budget, coilovers are still the way to go.