Yes it is. Having just one other person besides yourself brings tons of logistical benefits that lighten the load. You can have portals placed for you remotely instead of having to plan ahead for every last one of them. You can multiply how many boats of cargo can be moved at once. You can employ distraction tactics in combat so that the other player may more easily capitalise on opportunities for bonus damage.

I did my first playthrough solo but so much time gets sank into thoughtless toil. And of course when you are solo it is a shame to pour so much effort into building a structure that nobody else will get to appreciate.

I would strongly recommend playing with another player if for nothing but the more flowing pace.