HubSpot is the easiest inbound marketing/marketing automation software I've ever used. The user interface is consistently simple and clear. The support is high quality and you get answers quickly and in an organized fashion. It's relatively easy to onboard new sales or marketing employees. I love how integrated the CRM functions are with the inbound marketing/marketing automation functions. If you want a one-stop shop for CRM and inbound marketing, give HubSpot a serious look.
I'm a big fan, so there's not much about HubSpot I dislike. There's room for improvement in the number and sophistication of integrations with other software solutions, although this is true for most HubSpot competitors as well. There's also room for improvement in the granularity of the reporting.
We're solving the simplification of the marketing tech stack underpinning our lead generation and nurturing. HubSpot has helped us increase organic traffic as a percentage of total traffic, which has in turn led to a falling average cost per acquisition.