Nicki Minaj, Hammersmith Apollo, London

Risqué rapper hits high and low notes with a mix of feistiness and filth

Teenage girls, schoolboys, rockers, hip-hop lovers, mums, grandmas, and plenty of grown men: Nicki Minaj's screeching sold-out crowd is as diverse as the characters the Trinidad-born, Queens-raised rapper/singer shape-shifts through during her lengthy set.

"Before I even dreamt of coming here, I knew I would love you," she gushes during one of many emotional outbursts at this, the last night of her first-ever London shows to promote her 2012 album, Pink Friday: Roman Reloaded.

Cloaked in black, standing on top of dark staircases amid a set lit by flames and TV screens made to look like stained glass, Minaj – real name Onika Tanya Maraj – begins with a cage-rattling rendition of "Roman's Revenge".

In a flash, the random religious imagery is gone and Minaj – now flaunting her petite Barbie-doll figure in sparkling neon pink hot pants – is pure feistiness and filth as she barrels through "Did It On 'Em", "I Am Your Leader" and the spitting razor-sharp curses of "Beez in the Trap". The result is impressive. But when children in the crowd chant the X-rated lyrics from "Come on a Cone" back at a beaming bubblegum-sweet Minaj, the atmosphere turns more grotesque than gutsy. This time, the result is uncomfortable, and is just one of many contradictions in Minaj's performance, which veers wildly between tour de force mixtapes and dull DJ sets during her lengthy costume changes, sublime pop (especially on radio hit "Starships") and wet balladry, fearsome swagger and ridiculously amateurish choreography.

Minaj is also not ashamed of being "weird". The 29-year-old says she began creating alter egos when she was a child to escape from her less-than-rosy home life and is admirably open about her father's alcohol and drug problems. But onstage, the personas, such as her British character, Martha Zolanski (with dodgy accent), seem childish and half-baked.

When Minaj invites a group of her fans to the stage, it is clear she also enjoys her status as an unconventional role model. "It's kids like this that make me love what I do," she says with sudden sincerity.

The appeal of her many peaks and troughs – intriguing to start with – soon wears thin. Minaj – a shrewd businesswoman as well as an entertainer – may offer something potent to everyone, but it dilutes her undeniable charisma.

If she focused her talents, Nicki Minaj has what it takes to become a true superstar.