Is the HP E27u G5 good for gaming?

Only casually. It has no G-Sync or FreeSync and runs at 75 Hz with a 5 ms response, so fast-paced games will show motion blur and tearing.

Can one USB-C cable charge my laptop and carry video?

Yes. The USB-C connection handles display signal and power delivery to a compatible laptop, which is the main reason to pick this model over a plain HDMI monitor.

Is 27 inches too big for QHD?

No. At 2560x1440 the pixel density is about 109 ppi, which keeps text sharp without scaling at normal desk distance.

Does it work with a Mac?

Yes, over USB-C or HDMI. Mac users get the QHD resolution and sRGB colors, though macOS scaling behaves differently than on Windows.

The monitor, its stand, and the usual cables for setup. Check the listing for which video cable is included, since some bundles ship USB-C and others HDMI.

How does it compare with the older E27u G4?

The G5 keeps the 27-inch QHD IPS formula and updates the USB-C connectivity. It is an incremental office upgrade rather than a jump in panel speed or brightness.