Tessitura struggles to keep up with modern trends. So much so that they insist on including all new functionality (such as Resource Management, Dashboards, Bootstrap online ticketing templates... yeah in 2018 these are what Tessitura considers "modern") with every upgrade to try to meet every single business need in the organization, instead of improving upon, streamlining, and/or debugging existing functionality. The result is an incredibly messy and error-riddled product.
Their support staff is unhelpful at best and hostile at worst. Finding solutions to business questions (can we modify the price of one item in the cart based on the contents of the cart?) often involve the Help team upselling Tessitura Consulting packages to build "custom functionality" that not only costs an arm and a leg, but also is explicitly un-supported during the frequent upgrades, so you may end up paying thousands of dollars for them to build you a customization, then upgrade the system 6 months later and find that that customization no longer works and you're stuck either debugging it yourself or shelling out yet more money for them to fix it for you.
I have been a Tessitura user for 4 years and there has never been a period of peace: we're always weathering some kind of crisis: from online ticketing sales intermittently failing to tables full of data being lost when their Hosted Services handled an upgrade for us.
If you're a big shop and have the resources to maintain the system in-house, it's probably the best in the market. Just don't use their RAMP hosted service. If you're a mid- to small-size shop, I recommend looking elsewhere.