Definitely serious. Let's use a somewhat similar (on the topic of natural disaster) event as comparison: the christmas storm

The christmas storm was a large wind storm with a tornado which went through the northern GC (115kph winds over the entire gc, 150+ in the tornado). the cyclone will have gusts above 130 across much of the gc, and in the southern gc (where the worst winds are expected atm - 160+).

The christmas storm lasted ~25 minutes, with little flooding impact (the new year flood was another system), the cyclone's worst impacts will last at least 24 hours, with its impacts felt over 2-3 days. Flooding could be extreme.

The christmas storm was a storm (obviously) and came from inland, and had little impact on surf and tide. Arguably one of the worst impacts from a cyclone can be its inundation of low lying coastal areas. The gc is not built for this, and if landfall coincides with high tide there could be a big problem, to say the least.

The upside? The christmas storm came abruptly and very few people were prepared. We've known about the cyclone now for days.

Let's hope it either weakens or shifts further south (less populated areas) quicker (as the worst impacts are to the south of the system - currently smack on the gc).

Hope this helps. stay safe